TOKYO — It seems like only yesterday that President Trump and North Korean leader Kim Jong Un were exchanging affectionate letters and “love” was in the air.

But the bromance seems to be turning sour.

On Tuesday, Trump jokingly dusted off an old nickname for Kim, calling him “Rocket Man” for his keenness to test his weapons systems.

If it was a joke, Pyongyang didn’t get it.

North Korea responded angrily on Thursday by threatening to call Trump a senile dotard.

Analysts say images showing Kim Jong Un riding a white horse may signal preparations for a more confrontational stance with the international community. (Reuters)

The U.S. president “has lost politeness to the highest dignity of our republic and dared to use metaphors,” said Choe Son Hui, North Korea’s vice foreign minister, according to the Korean Central News Agency.

Trump also said this week that the United States is prepared to use its military against North Korea if it has to, which has also angered Pyongyang.

“It would be a very dangerous challenge if it was a deliberate reappearance of expressions reminiscent of two years ago when the war of words went back and forth across the ocean,” Choe said.

North Korea's state-run television aired video of Kim Jong Un celebrating the completion of a new 'socialist utopia' despite the country's dismal economy. (Reuters)

She then unleashed an insult in return — or the threat of one, which comes to the same thing.

“If he uses statements and expressions that intentionally amplify the atmosphere of confrontation at this time of crisis, we will have to diagnose that the dotard started to be senile again,” she said.

Choe said the foreign ministry “cannot contain its displeasure toward President Trump’s remark that was blurted out in an inappropriate manner at a highly sensitive time.” It would be fortunate, she said, if the threat to use force “and the metaphor was a spontaneous slip of the tongue, but the problem would be different if it was a deliberate provocation.”